Scientists Have Decoded the Secret History of the Mysterious ‘Tree of Life’
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The Baobab is one of the strangest-looking trees on Earth, and has been described as an “upside-down tree” and even the “tree of life” due to its nutrient-rich fruit.
While six of the eight species of baobabs thrive on the island nation of Madagascar, scientists have never been 100 percent sure of their origin, as the trees don’t appear in the fossil record.
After immense genetic study of all extant species, a new study confirms that the ‘tree of life’ originated in Madagascar, and that one particular species made an incredible dispersal journey to Australia.
For 400 million years, trees have grown and diverged into some 73,000 species worldwide. There’s the skyscraping enormity of the coastal redwoods (Sequoia sempervirens), the mind-boggling diminutive size of the dwarf willow (Salix herbacea), and nearly every imaginable size and shape in between. However, arguably the most perplexing genus in the plant kingdom is Adansonia, also known as the baobab tree.
Consisting of eight species spread across Africa, Madagascar, Asia, and Australia, this genus is usually defined by its chunky trunk and relatively small canopies, which together give it the overall impression of an “upside-down tree.” It’s also known as the “tree of life” for its ability to product nutrient dense fruit in the dry season.
This species of tree—found in dozens of African countries alone and first described by ancient Egyptians—is the subject of many tales and local folklore, and its prominence in human culture spurred a husband-and-wife research team to uncover the 21 million-year-long journey of this tree through its genetics. The results of the research were published in the journal Nature earlier this week.
“This project uncover[ed] patterns of baobab speciation in Madagascar followed by the astonishing long-distance dispersal of two species, one to Africa and another to Australia,” Queen Mary University of London’s Andrew Leitch, a co-author on the study, said in a press statement. His wife, Ilia Leitch, a fellow co-author and expert at the Royal Botanic Gardens Kew, added that “this work has uncovered new insights into the patterns of speciation in baobabs and shows how climate change has influenced baobab distribution and speciation patterns over millions of years.”
Apart from their almost otherworldly stature, baobabs have another strange attribute—their distribution. While most baobabs reside in Africa, and especially in the island nation of Madagascar, one species of a baobab (Adansonia gregorii) sprouts on the unlikely continent of Australia.
Andrew and Ilia Leitch, along with the rest of the research team, analyzed the genomes of the eight extant Adansonia species, including everything from the absolutely gargantuan Adansonia grandidieri to the Australia-based A. gregorii. Because Adansonia has no fossil record, scientists have been unsure of its place of origin, but this new study confidently states that the baobab evolved on what is now Madagascar some 21 million years ago.
Of course, this leads to another question: how did the tree somehow wind-up in Africa—and even more perplexingly, Australia, which is roughly 5,500 miles away? After all, the arrival of the baobab tree occurred after the break up of Gondwana, a supercontinent that contained two-thirds of today’s landmass. The researchers theorize that the tree must’ve accomplished a long-distance dispersal event to the Land Down Under, which can be seen via evidence of a genetic bottleneck in the A. gregorii species.
After analyzing these baobabs, the researchers are also calling for stronger protections of these trees across the board and even theorize that the species A. suarezensis in northern Madagascar could even go extinct by 2080. While baobabs have inspired humans for millennia, it’s now up to us to make sure they survive and inspire many more generations in the future.
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